Process analyzer for monitoring electrochemical deposition solutions

ABSTRACT

The present invention relates to a process analyzer for analyzing composition of sample electrochemical deposition solutions, comprising at least one microelectrode having a radius of not more than about 5 μm. The process analyzer preferably comprises: (1) two or more independent analytical modules for analyzing fluid samples, (2) a primary manifold communicatively connected to the analytical modules for introducing fluid samples thereinto, and (3) a computational device communicatively associated with the analytical modules for colleting and processing analytical data therefrom, and therefore can be used to conduct automatic and simultaneous analysis of two or more sample solutions.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This is a continuation-in-part of U.S. patent application Ser.No. 09/690,770 filed Oct. 17, 2000, which is in turn acontinuation-in-part of U.S. patent application Ser. No. 09/421,658filed Oct. 20, 1999, now issued as U.S. Pat. No. 6,280,602.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention in a broad aspect relates to analyticaltools for monitoring electrochemical deposition (ECD) solutions, andmore specifically to a process analyzer comprising microelectrodes forcomposition analysis of various metal electroplating solutions.

[0004] 2. Related Art

[0005] Conventional ECD process analyzers use rotating disk electrodes(RDEs), for providing a well-defined flow of ECD solution towards thesurface of such rotating disk electrodes, so as to provide strongeranalytical signals (for example, the plating current).

[0006] When a rotating disk electrode rotates in a metal electroplatingsolution, it generates a flow pattern akin to a vortex that sucks thesolution as well as analyte therein toward it. The layer of solutionthat is immediately adjacent to the surface of the rotating diskelectrode behaves as if it were “stuck” to such electrode, i.e., whilethe bulk of the metal electroplating solution is being stirredvigorously by the rotating disk electrode, this thin layer of solutionmanages to cling to the surface of the electrode. Therefore, this thinlayer of solution is generally referred to as “the stagnant layer” or“the boundary layer.”

[0007] The metal electroplating solution and the analyte therein areconveyed to the surface of the rotating disk electrode by two types ofmotions: (1) the vortex flow generated by rotation of the RDEcontinuously brings fresh solution and analyte therein to the outer edgeof the stagnant layer; and (2) the solution and analyte therein at theouter edge of the stagnant layer move across such stagnant layer viamolecular diffusion. Therefore, the thinner the stagnant layer, thefaster the solution and analyte therein can diffuse across it and reachthe surface of the rotating disk electrode, and the higher the electriccurrent measured by the RDE.

[0008] For generating a sufficiently thin stagnant layer, the RDE isgenerally operated at a rotating speed above 800 rpm, rendering such RDEprone to mechanical breakdown after continuous operation. Moreover, theconventional RDE usually has a diameter of from about 1.5 mm to about 10mm, in order to ensure structural integrity and reliability at such highrotating speed. Therefore, an ECD process analyzer that comprises aplurality of such conventional rotating disk electrodes is inevitablebulky in size.

[0009] Finally, when using such bulky ECD process analyzer, a largevolume of sample metal electroplating solution has to be used in orderto obtain sufficient analytical signals, generating a large amount ofwaste solution.

[0010] It would therefore be a significant advance in the art, and isaccordingly an object of the present invention, to provide an ECDprocess analyzer comprising electrodes that are resistant to mechanicalbreakdown, small in size, and generating minimum amount of wastesolution during solution analysis.

[0011] It is another object of the present invention to provide anautomated analytical platform that comprises multiple analysis modulessuitable for various kinds of fluidic analyses, preferably including atleast one ECD process analyzer as described hereinabove.

[0012] Other objects and advantages will be more fully apparent from theensuring disclosure and appended claims.

SUMMARY OF THE INVENTION

[0013] The present invention in a broad aspect relates to a processanalyzer for analyzing composition of sample electrochemical depositionsolutions, comprising at least one microelectrode having a radius of notmore than 5 μm.

[0014] In a specific embodiment of the present invention, the processanalyzer comprises one or more analytical modules for analyzing fluidsamples, a primary manifold communicatively connected to the analyticalmodules for introducing fluid samples thereinto, and a computationaldevice communicatively associated with the analytical modules forcollecting and processing analytical data therefrom. Preferably, atleast one of the analytical modules is a microelectrode cell thatcomprises a test electrode, a current source electrode, and a referenceelectrode, and the test electrode is a microelectrode that has a radiusof not more than about 5 μm.

[0015] Additional aspects, features and embodiments of the inventionwill be more fully apparent from the ensuing disclosure and appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a top view of a process analyzer according to oneembodiment of the present invention.

[0017]FIG. 2 is a side view of the process analyzer of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION, AND PREFERRED EMBODIMENTS THEREOF

[0018] U.S. patent application Ser. No. 09/421,658 for “Method andApparatus for Determination of Additives in Metal Plating Baths,” asfiled on Oct. 20, 1999 and issued as U.S. Pat. No. 6,280,602, disclosesan analytical cell for conducting Pulsed Cyclic Galvanostatic Analysis(PCGA), the contents of which are incorporated hereby in their entiretyfor all purposes.

[0019] Conventional ECD process analyzers employ rotating diskelectrodes in the PCGA cell to stir the electrolyte solution containedin such cell, for increasing the accuracy and consistency ofmeasurements across PCGA cycles.

[0020] However, the rotating disk electrodes are vulnerable tomechanical breaking-down, when continuously operated at high rotatingspeed, as generally required by PCGA analysis.

[0021] Therefore, the present invention employs a microelectrode inplace of the conventional rotating disk electrode in the ECD processanalyzer. A microelectrode is defined hereby as an electrode having aradius of not more than 5 microns.

[0022] One major advantage of using such microelectrode is it is moreresistant to mechanical breaking-down, in comparison to the conventionalrotating disk electrode, because such microelectrode does not comprisemoving parts and is devoid of rotatory motion.

[0023] Such microelectrode also allows for a much higher flux to theelectrode surface, either by migration or diffusion, which providessufficiently stronger analytical signals (such as current densities)than those provided by a rotating disk electrode.

[0024] For example, while using a microelectrode having a hemisphericaltip and a radius of approximately 5 microns to obtain a steady stateconcentration profile in a concentration polarized system, thecalculations show that the concentration of a target oxidized or reducedspecies at a distance of about 25 microns from the electrode isapproximately 90% of the bulk concentration of said oxidized or reducedspecies. Such distance is only about ¼ of the thickness of the stagnantlayer of a rotating disk electrode spinning at 955 rpm. The size of themicroelectrode may be tailored to provide a much stronger flux to theelectrode surface than the conventional rotating disk electrode byshrinking the radius. Similarly an array of various sizedmicroelectrodes in the same electrochemical cell can be multiplexed inreal time to vary the effective size and hence comparable rotation speedin real time.

[0025] The time required for a hemispherical microelectrode to reachsteady state, after stepping the measurement potential to a givenvoltage, can be approximately calculated according to the followingequation:

t _(ss)=2500×r ₀ ² /πD

[0026] wherein t_(ss) is the time in which the electric current measuredis only 2% greater than the steady state electric current, r₀ is theradius of the microelectrode, and D is the diffusion coefficient of thetarget species (typically 10⁻⁵ cm²/s).

[0027] According to the above equation, when the radius of themicroelectrode is about 5 microns, t_(ss) is about 25 seconds, and whenthe radius is about 1 micron, t_(ss) is about 1 second.

[0028] For very short duration experiments, which are possible withultra-microelectrodes, on the order of less than 60 microseconds for a5-micron electrode, where the diffusion layer is less than r_(o), thecurrent relationship is Cottrell like:$i = \frac{{nFACoDo}^{1/2}}{\pi^{1/2}t^{1/2}}$

[0029] where D and C refer to concentration of the species of interestand that species diffusion coefficient.

[0030] The signal to noise for ultra-microelectrodes is enhanced overthat of a conventional electrode by virtue of the fact that the lowcurrents employed minimize uncompensated iR drops due to liquidresistance and two electrode systems may thus be used, minimizing straycurrent and environmental noise pickup.

[0031] Therefore, the use of a microelectrode with a radius of not morethan 5 microns, preferably not more than 1 micron, not only provides astronger analytical signal, but also enables quicker measurement of thesample solution, by allowing the steady state to be achieved faster, incomparison with use of the conventional rotating disk electrode.

[0032] Moreover, a process analyzer using microelectrodes can havesignificantly reduced size in comparison to one using conventionalrotating disk electrodes, in light of the fact that the average diameterof the RDE is about 3 mm to about 10 mm, which is about 300 to about5000 times larger than that of the microelectrode disclosed herein.Therefore, use of the microelectrodes enables such process analyzer tohave much smaller footprint than that using conventional rotating diskelectrode.

[0033] Further, multiple microelectrodes may be packed into a compactunit that comprises multiple analytical cells or modules forcomplimentary or simultaneous fluid measurements.

[0034] Finally, the microelectrodes allow measurement of fluid samplesof very small volume, due to the small physical size of such electrodes,therefore resulting in less amount of waste.

[0035] In fact, the current analysis of organic additives in the highacid and low acid Viaform® chemistry, using a process analyzercomprising the microelectrodes, showed better results than the priorprocess analyzer that uses rotating disk electrodes.

[0036] The microelectrode as described hereinabove may comprise carbonfibers or platinum fibers. In a preferred embodiment, suchmicroelectrode has a composite structure, with an inner electricallyconductive metal core, and an outer dielectric layer formed byoxidization of a metal or metal alloy including metals such as tantalum,niobium, zirconium, hafnium, and titanium.

[0037] A PCGA-based process analyzer usually comprises a testingelectrode, a current source electrode, and a reference electrode. It ispreferred that at least the testing electrode is a microelectrode asdefined hereinabove. It is more preferred that all the electrodes insuch process analyzer are microelectrodes.

[0038] A preferred embodiment of the present invention relates to amulti-cell process analyzer, which comprises one or more analyticalmodules for analyzing fluid samples, a primary manifold communicativelyconnected to the analytical modules for introducing fluid samplesthereinto, and a computational device communicatively associated withthe analytical modules for collecting and processing analytical datatherefrom.

[0039]FIG. 1 shows an example of such multi-cell process analyzer 100,which comprises four analytical modules 102, 104, 106, and 108 foranalyzing various fluid samples. Specifically, analytical module 102 isa microelectrode cell that comprises at least one microelectrode asdescribed hereinabove; analytical module 104 comprises a photometer forconducting spectroscopic analysis; analytical module 106 is a KarlFischer cell for conducting Karl Fischer coulometry; and analyticalmodule 108 is a high volume E-cell.

[0040] The analytical modules 102, 104, 106, and 108 are independent ofone another, and they therefore are capable of conducting simultaneousfluid measurement or analysis. Such analytical modules are independentlycontrolled by a microcontroller 105. A microcontroller is an inexpensivesingle-chip computer, which is capable of storing and running a program,and the PICO microcontrollers manufactured by Microchip Technology(Chandler, Ariz.) are preferably employed for the purpose of controllingthe analytical modules of the present invention. Additional analyticalmodules can be added for conducting PCGA, spectroscopic, potentiometric,and other traditional ECD solution measurements.

[0041] The process analyzer 100 also comprises a primary manifold 120,which is communicatively connected to the analytical modules forintroducing fluid samples into such modules. The primary manifold 120may comprise various pumps, valves, and fluidic tubing and pathway.Preferably, such primary manifold 120 employs variable volumedisplacement pumps, face-sealed valves, and pre-manufactured fluidicpathways, for the purpose of reducing the footprint of such manifold. Itis also desirable to have such primary manifold 120 being mechanicallyattached to the analytical modules, so as to further reduce discreteplumbing required for conventional fluid manifolds used in ECD processanalyzers.

[0042] For example the primary manifold 120 in FIG. 1 comprises 6variable volume displacement pumps 122, with slots 123 for two more. Italso comprises multiple valves 126 (as shown in FIG. 2), which mayinclude face-sealed valves for pump flow control, two-way valves forCDA/N₂/water, and three-way valves for fluid diversion. Moreover, suchprimary manifold 120 comprises a make/break plate 130 havingpre-manufactured fluid pathways thereon.

[0043] The process analyzer 100 further comprises a computational device150 that is communicatively associated with the analytical modules forcollecting and processing analytical data therefrom.

[0044] Such computational device 150 can be a microprocessor, or apersonal computer, or an on-line data analysis system.

[0045] In one preferred embodiment of the present invention, the primarymanifold 120 comprises a serial port 140 for connecting themicrocontrollers 105 of the analytical modules with the computationaldevice 150. One preferred serial port suitable for the purpose ofpracticing the present invention is an RS-485 driver board, which can bedirectly snapped onto the pumps 122. Such RS-485 driver board morepreferably independently addresses each analytical module.

[0046] The computational device 150 preferably uses QNX software systemfor ensuring stability. It may comprise a low level interface to allowcontrol of individual analytical modules for new applications, and ahigh level interface for processing and outputting analytical data to acentral control network.

[0047] Such process analyzer as described hereinabove has significantlyreduced size in comparison to conventional process analyzers. Forexample, a conventional copper ECD, organic wet tray has a standard sizeof 8″×15″×17″, and a copper ECD organic wet tray designed according tothe present invention has a size of 4″×6″×7″.

[0048] The decreased size of the process analyzer will significantlyreduce sample and analyte consumption during the fluid analysis process.

[0049] Although the invention has been variously disclosed herein withreference to illustrative embodiments and features, it will beappreciated that the embodiments and features described hereinabove arenot intended to limit the scope of the invention, and that othervariations, modifications and other embodiments will suggest themselvesto those of ordinary skill in the art. The invention therefore is to bebroadly construed, consistent with the claims hereafter set forth.

What is claimed is:
 1. A process analyzer for analyzing composition ofsample electrochemical deposition solutions, said process analyzercomprising at least one microelectrode having a radius of not more thanabout 5 μm.
 2. The process analyzer of claim 1, wherein themicroelectrode has a radius of not more than 1 μm.
 3. The processanalyzer of claim 1, wherein the microelectrode has a hemispherical tip.4. The process analyzer of claim 1, wherein the microelectrode comprisescarbon fibers.
 5. The process analyzer of claim 1, wherein themicroelectrode comprises platinum fibers.
 6. The process analyzer ofclaim 1, wherein the microelectrode has a composite structure, includingan inner electrically conductive metal core, and an outer dielectriclayer formed by oxidization of a metal or metal alloy including at leastone metal selected from the group consisting of tantalum, niobium,zirconium, hafnium, and titanium.
 7. The process analyzer of claim 1,wherein the microelectrode is non-rotational in relation to othercomponents of said process analyzer.
 8. The process analyzer of claim 1,comprising a test electrode, a current source electrode, and a referenceelectrode, wherein the test electrode is a microelectrode that has aradius of not more than about 5 μm and is non-rotational in relation toother components of said process analyzer.
 9. The process analyzer ofclaim 1, comprising one or more analytical modules for analyzing fluidsamples, a primary manifold communicatively connected to said analyticalmodules for introducing fluid samples thereinto, and a computationaldevice communicatively associated with said analytical modules forcollecting and processing analytical data therefrom.
 10. The processanalyzer of claim 9, comprising at least two analytical modules that areindependent of one another, so that said process analyzer is capable ofsimultaneously analyzing at least two sample electrochemical depositionsolutions.
 11. The process analyzer of claim 9, wherein at least one ofsaid analytical modules is a microelectrode cell that comprises a testelectrode, a current source electrode, and a reference electrode, andwherein said test electrode comprises a microelectrode that has a radiusof not more than about 5 μm.
 12. The process analyzer of claim 9,comprising at least one analytical module selected from the groupconsisting of Pulsed Cyclic Galvanostatic Analysis (PCGA) modules,spectroscopy modules, potentiometry modules, and Karl Fischer coulometrymodules.
 13. The process analyzer of claim 12, comprising a PulsedCyclic Galvanostatic Analysis (PCGA) module, wherein said PCGA modulecomprises a microelectrode that has a radius of not more than about 5μm.
 14. The process analyzer of claim 10, wherein said one or moreanalytical modules are independently controlled by one or moremicrocontrollers.
 15. The process analyzer of claim 9, wherein theprimary manifold comprises one or more variable volume displacementpumps.
 16. The process analyzer of claim 9, wherein the primary manifoldcomprises one or more face-sealed valves.
 17. The process analyzer ofclaim 9, wherein the primary manifold comprises one or more two-wayvalves and/or three-way valves.
 18. The process analyzer of claim 9,wherein the primary manifold comprises a make/break plate havingpre-manufactured fluid pathways thereon.
 19. The process analyzer ofclaim 9, wherein the one or more analytical modules are controlled byone or more microcontrollers, and wherein the primary manifold comprisesa serial port for connecting said microcontrollers with thecomputational device, so as to enable communicative associationtherebetween.
 20. The process analyzer of claim 19, wherein the primarymanifold comprises one or more variable volume displacement pumps, ontowhich said serial port is attached.
 21. The process analyzer of claim 9,wherein the computation device outputs the collected and processedanalytical data to a central control network.